Method for preparing polyether polyols

ABSTRACT

Polyether polyols can be prepared by reacting polyols with epoxides in the presence of basic catalysts, by treating the polyether polyols containing the basic catalysts with OH-functional solid compounds of metals of groups III to VIII of the periodic system of the elements (Mendeleyev), the compounds being insoluble in the polyether polyols and having BET surface areas of from 10 to 1000 m 2 /g, isolating the solid inorganic compounds laden with the basic catalysts from the polyether polyol and using them in the reaction of polyols with epoxides, or bringing the isolated inorganic compounds laden with the basic catalysts into contact with the polyols that are to be used in the reaction with epoxides, separating those polyols from the inorganic compounds and delivering them to the reaction with epoxides.

This application is a 371 of PCT/EP98/04860, filed Aug. 5, 1998.

The present invention relates to a process for the preparation ofpolyether polyols by reacting polyols with epoxides in the presence ofbasic catalysts, by removing the bases from the polyethers by means ofOH-functional solid inorganic metal compounds, returning the base-ladencompounds to the reaction of polyols with epoxides or treating thebase-laden compounds with polyols and using those polyols in thereaction with epoxides.

From U.S. Pat. No. 3,528,920 it is known to remove basic catalysts usedin the preparation of polyether polyols from the polyether polyols. Inorder to remove the basic catalysts, the polyether polyols wereneutralised with sulfuric acid then treated with magnesium silicate,dried and subsequently distilled at elevated temperature in order toremove water. The magnesium silicate was then separated from the polymerproduct in a separate step.

U.S. Pat. No. 4,029,879 discloses an improved process for removing basiccatalysts from polyether polyols by treating the polyether polyols withmagnesium silicate in the presence of from 1 to 5 wt. % water. In aseparate step, the adsorbent must then be separated from the polyetherpolyol by filtration and the water must be separated off bydistillation.

Disadvantages of the above-mentioned processes are the large number ofpurification steps, the use of acids for neutralisation, and theformation of unrecoverable, economically and ecologically unsound,contaminated magnesium silicate waste. Owing to the known processes forremoving catalysts from polyether polyols, which are associated with thedescribed disadvantages, the processes used hitherto are not veryeconomical.

The object of the present invention is to make available an economicallyand ecologically advantageous process for removing basic catalysts frompolyether polyols, which avoids the disadvantages of the knownprocesses.

The present invention provides a process for the preparation ofpolyether polyols by reacting polyols with epoxides in the presence ofbasic catalysts, which process is characterised in that the polyetherpolyols containing the basic catalysts are treated with OH-functionalsolid compounds of metals of groups III to VIII of the periodic systemof the elements (Mendeleyev), the said compounds being insoluble in thepolyether polyols and having BET surface areas of from 10 to 1000 m²/g,the solid inorganic compounds laden with the basic catalysts areisolated from the polyether polyol and used in the reaction of thepolyols with epoxides, or the isolated inorganic compounds laden withthe basic catalysts are brought into contact with the polyols that areto be used in the reaction with epoxides, those polyols are separatedfrom the inorganic compounds and delivered to the reaction with theepoxides.

The preparation of polyether polyols has long been known and isdescribed in general terms, for example, in Kunststoffhandbuch, Volume7, Polyurethane, Carl Hanser Verlag, Munich-Vienna, 1973, p. 58 ff. Allknown polyols come into consideration as starter compounds for theepoxide polymerisation. Special mention may be made of mono-, di-, tri-and tetra-ethylene glycol, mono-, di-, tri- and tetrapolypropyleneglycol, 1,2-, 1,3-, 1,4-butanediol, glycerol, trimethylolpropane,trimethylolethane, pentaerythritol, hexanetriol, sugars, such assaccharose, fructose, maltose, sucrose, xylose, sorbitol, palatinitol,xylitol, oxyalkylation products of ammonia and amines, such asethylenediamine, diethylenetriamine, piperazine, aniline,toluylenediamine, methylenedianiline, phenols such as hydroquinone,resorcinol, pyrocatechols, bisphenol F, bisphenol A and theiroxyalkylation products, and also so-called prepolymers, which areobtained by reacting the above-mentioned polyols with from 0.5 to 4 mol,preferably from 0.7 to 2 mol, of epoxide/mol of polyol.

There are preferably used mono- to tetra-ethylene glycol, mono- totetra-propylene glycol, glycerol, trimethylolpropane, pentaerythritoland the above-mentioned sugars and their hydrogenation products.

Suitable epoxides are ethylene oxide, propylene oxide, butylene oxide,cyclohexene oxide, styrene oxide and mixtures of those epoxides.Ethylene oxide and propylene oxide are preferred.

There are used as basic catalysts especially potassium hydroxide andsodium hydroxide.

As mentioned above, the basic catalysts remain in the polyether polyolswhen the polyether polyols are prepared and must be removed therefrom.

By the process according to the invention it is now possible to removethe basic catalysts by treating the polyether polyols containing thebasic catalysts with OH-functional solid compounds of metals of groupsIII to VIII of the periodic system of the elements, the said compoundsbeing insoluble in the polyether polyols. There may be mentioned asOH-functional compounds of metals preferably the hydroxides and hydroxyoxides of aluminium, gallium, silicon, tin, titanium, zirconium,hafnium, tantalum, niobium and iron, especially the hydroxides andhydroxy oxides of aluminium, silicon, tin, titanium, zirconium, tantalumand niobium, very especially of aluminium, silicon, titanium, tantalumand niobium. Of course, the hydroxides and hydroxy oxides of thementioned metals may also be used in the form of chemical compounds orin mixtures with one another. Mention may be made of, for example,aluminium-silicon hydroxy oxides and titanium-zirconium hydroxy oxides.

It is also possible to mix the mentioned hydroxides and hydroxy oxideswith other metal compounds, such as magnesium silicates or aluminiumtitanates, as well as with layered silicates of the montmorillonite,bentonite and (hydro)talcite type. The amount of such admixed metalcompounds is, depending on the procedure, up to 500 parts by weight,preferably 200 parts by weight, based on 1 part by weight of basiccatalyst.

Very special preference is given to the use of the hydroxy oxides of theabove-mentioned metals.

The amount of the above-mentioned solid inorganic compounds to be usedis up to 1000 parts by weight, preferably up to 400 parts by weight,based on 1 part by weight of basic catalyst.

The adsorbents of the above-described type used in the process accordingto the invention for removing the basic catalysts are described, forexample, in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition,Vol. A1, 557 ff; A27, 74 ff; A20, 190-271 and 297-311; A24, 12 ff; A26,78 ff; A17, 255 ff; A23, 583-791.

The adsorbents used have a BET surface area of from 10 to 1000 m²/g,preferably from 20 to 900 m²/g, especially from 25 to 800 m²/g. They canbe used as powders or in the form of course-ground material, granules,spheres, cylindrical bodies, hollow cylindrical bodies, or rings. TheOH-functional surfaces of the mentioned hydroxides and hydroxy oxidesare obtained especially by suitable methods of calcining precipitatedhydroxy oxides of the mentioned metals or their gel-like hydrates atrelatively low temperatures. The preparation of such surface-richhydroxides and hydroxy oxides of the above-mentioned metals is known andis described, for example, in Kirk Othmer, Encyclopedia of ChemicalTechnology, 3rd edition, Vol. 2, p. 218 ff (1978); Ullmann'sEncyclopedia of Industrial Chemistry under the metal names indicatedabove.

In the preparation of polyether polyols there are used as basiccatalysts in addition to potassium and sodium hydroxide mentioned abovealso the hydroxides of the other alkali metals and those of the alkalineearth metals, although to a lesser degree. In addition, it is possibleto use as basic catalysts tertiary amines, such as triethylamine,tributylamine, tetramethylethylenediamine,pentamethylenediethylenetriamine, diethylpiperazine,methyl-diaza-bicycloundecene, methyl-diaza-bicyclononene andpentamethylguanidine.

Implementation of the process according to the invention involves inprinciple the following operations:

reaction of the polyols with epoxides in the presence of basic catalyststo form polyether polyols,

treatment of the polyether polyols with the OH-functional, solid,insoluble, inorganic metal compounds,

separation of the polyether polyols from the solid metal compoundscontaining the basic catalysts,

treatment of the metal compounds isolated from the polyether polyols andcontaining the basic catalysts with the polyols provided for reactionwith epoxides,

reaction with the epoxides.

In technical terms it is possible to carry out those basic operations invarious ways, either in a discontinuous, a semi-continuous or a fullycontinuous procedure.

All operations and procedures are preferably carried out at temperaturesof from 80 to 190° C., especially from 100 to 180° C., and at from 0.5to 20 bar, preferably from 0.8 to 15 bar, and it is entirely possible toconduct the individual operations within a procedure at differenttemperatures and pressures.

The amount of polyols for treating the metal compounds containing thebasic catalysts can readily be determined by appropriate tests and,depending on the procedure and the catalyst content of the metalcompound, may be from 1 to 200 times, preferably from 3 to 150 times,especially from 5 to 100 times, the amount of catalyst with which themetal compound is laden.

In a particular form, discontinuous operation may be, for example, asfollows: in a reactor, the reaction of polyol with epoxides in thepresence of a basic catalyst is carried out in a known manner, excessepoxide is driven off after the reaction, a suitable amount of a metalcompound to be used according to the invention is added and thepolyether polyol is treated therewith, then the metal compound ladenwith catalyst is separated from the polyether polyol by filtration,centrifugation or another separating operation and that filtration orcentrifugation residue is introduced into the reactor and the nextreaction of polyol with epoxide is catalysed therewith. It is alsopossible to treat the catalyst-containing residue with the appropriateamount of the polyol that is to be used for the next batch, remove thecatalyst therewith, separate off the metal compound and use the polyol,which now contains catalyst, in the reaction with epoxide.

In a specific embodiment, a semi-continuous procedure may be carriedout, for example, as follows:

From a storage container, polyol or a prepolymer (prepared from thepolyol by addition of only a few mol of epoxide per mol of polyol) (PL)is introduced into at least one vessel I containing a bed of the metalcompound, which bed is largely saturated with catalyst and stillcontains polyether polyol (PE). PL passes into the bed, drives the PEthat is still present out of the bed and removes the catalyst from themetal compound. When PE has left the bed in the direction towards acollecting vessel, the stream of PL is passed into a reaction zone andreacted with the desired amount of epoxide. Residues of unreactedepoxide are blown out and the PE obtained is passed into at least onevessel II which, analogously to I, contains a bed of the metal compound,but that bed is free or largely free of catalyst. As it passes throughII, the PE is freed of catalyst and collected. That entire procedure canbe repeated until I is depleted of catalyst and II is largely saturatedwith catalyst. The direction of flow is then reversed, PL is passedthrough II, the reaction is carried out in the reaction zone and thecatalyst is retained in I. The PL that is initially still present in Iis expelled from the bed by the incoming PE and is ready for furtherreactions.

Another particular embodiment of the process according to the inventionis a fully continuous procedure and it may be so arranged that in theabove-mentioned semi-continuous process, the reaction zone is also setup for continuous operation and is used accordingly:

From a storage container, therefore, PL is passed continuously throughat least one bed of the metal compounds (I) that is largely saturatedwith catalyst, is reacted continuously with epoxide in the reactionzone, and then PE is continuously freed of catalyst in at least onesecond bed (II) containing metal compound. When bed I is depleted ofcatalyst and bed II is largely saturated, the direction of flow isreversed and PL is passed through II, reacted with epoxide again in thereaction zone and separated from the catalyst in I.

Of course it is possible in the various procedures to allow the reactionwith epoxides also to take place partially in the beds containing themetal compound.

The reaction zone may be constructed of different apparatuses and mayconsist of, for example, a stirrer vessel cascade, chamber reactors,reaction tubes with plug flow and mixing elements, of reactiondistillations, which also permit the removal, in parallel with thereaction, of allyl alcohol and excess epoxide, and other reactorssuitable for continuous liquid/gas reactions, as are described ingreater detail, for example, in Ullmann's Encyclopedia of IndustrialChemistry, 5th edition, Vol. B4, 87 ff, 99 ff, 106-328, 561 ff and Vol.B3, 7-5 to 7-10, and Perry's Chemical Engineers Handbook, 6th edition,4-24 to 4-52.

Depending on the nature and form of the adsorbent and of the resistanceto flow associated therewith, the vessels for the adsorbent bed may beslim columns with a deep adsorbent bed or, alternatively, broaddrum-like containers with a flat bed through which material can floweasily. In order to avoid back-mixing, the inlet and outlet regions are,for example, to be conical in shape and filled with filling material.

The above descriptions of particular embodiments of the processaccording to the invention show that the basic catalysts

are retained over a prolonged period and are not destroyed byneutralisation,

are removed from the polyether polyol in a very simple manner, withoutthe need for additional means and energy, and

no longer appear and have to be handled outside the actual productionunit.

EXAMPLES Example 1

440 g of a solution of a polyether, prepared from 3% trimethylolpropane(wt. %), 80% propylene oxide and 17% ethylene oxide having a molecularweight of 4800 and an OH number of 35, containing 0.25% potassium intoluene (1/1), were stirred for one hour at 85° C. with 32 g of analuminium oxide hydrate (Camag 5016/A). After filtering off withsuction, washing with toluene and drying, the aluminium oxide hydratecontained 1.3% potassium and the polyether contained 61 ppm ofpotassium.

On treating the isolated aluminium oxide with a 3.8-fold amount ofglycerol at 85° C. for one hour, its potassium content fell by 74% andthe glycerol then contained 0.14% potassium.

This Example shows, in the first part, that KOH is removed virtuallyquantitatively from a catalyst-containing polyether polyol by means ofan aluminium oxide and, in the second part, that ¾ of the adsorbedamount of KOH is desorbed from that aluminium oxide again by simpletreatment with the polyol glycerol.

Example 2

When Example 1 was repeated without toluene using 220 g of polyether and32 g of aluminium oxide, 103 ppm of potassium remained in the polyether.

Example 3

When Example 1 was repeated using a silicon dioxide (Grace 432), nopotassium (<1 ppm) was found in the polyether. When Example 2 wasrepeated using the above silicon dioxide, 10 ppm of potassium were foundin the polyether.

This Example shows that the various metal compounds have differenteffects under comparable conditions.

Example 4

50 g of prepolymer consisting of approximately 70 wt. %trimethylolpropane and 30 wt. % propylene oxide (which had been freed ofKOH) were gassed with propylene oxide for 12 hours in a 250 mlthree-necked flask, with vigorous stirring at 250 rpm, at from 100 to120° C. and at normal pressure, together with 5 g of Al₂O₃ which camefrom a polyether polyol purification and contained 1.2 wt. % potassium.The increase in mass as a result of the polymerisation of propyleneoxide was 17 wt. %.

Example 5

When Example 4 was repeated using an Al₂O₃ from a PE purification thatcontained 2.3 wt. % potassium, an increase in mass of 196 wt. % wasobtained as a result of the polymerisation of propylene oxide.

Comparison Examples 6 and 7

When Example 4 was repeated without addition or with pure Al₂O₃,polymerisation of propylene oxide was not observed.

Examples 4 and 5 prove that the KOH-laden metal compounds as such,without previously being treated separately with polyol, catalyse thereaction of polyols with epoxides. According to Comparison Examples 6and 7, no reaction takes place without addition and with pure aluminiumoxide.

What is claimed is:
 1. A process for the preparation of polyetherpolyols comprising reacting polyols with epoxides in the presence ofbasic catalysts, wherein the polyether polyols containing the basiccatalysts are treated with OH-functional solid compounds comprising: (i)the hydroxides of aluminum, gallium, silicon, tin, titanium, zirconium,hafnium, tantalum, niobium or iron; (ii) the hydroxy oxides of aluminum,gallium, silicon, tin, titanium, zirconium, hafnium, tantalum, niobiumor iron; or (iii) mixtures thereof; wherein the OH-functional solidcompounds are insoluble in the polyether polyols and have BET surfaceareas of from 10 to 1000 m²/g; the solid inorganic compounds laden withthe basic catalysts are isolated from the polyether polyol and used inthe reaction of polyols with epoxides, or the isolated inorganiccompounds laden with the basic catalysts are brought into contact withthe polyols that are to be used in the reaction with epoxides, thosepolyols are separated from the inorganic compounds and delivered to thereaction with epoxides.
 2. The process of claim 1, characterized in thatthe solid inorganic compounds are used in amounts of up to 1000 parts byweight, based on 1 part by weight of basic catalyst.